Sixteen bodies were found on board a crowded dinghy floating south of Lampedusa, while another person died shortly after the arrival of rescuers.
The majority are thought to have died from dehydration and hyperthermia, the Italian Navy said.
One person suffering acute hypothermia was flown by helicopter to Lampedusa, while the 74 other passengers were helped on board a navy ship.
A total of 278 boat migrants were picked up by the authorities on Thursday, as people continue to make the perilous sea journey despite heightened risks during the winter months.
Speaking in Rome on Friday, Foreign Minister Paolo Gentiloni said more action was needed to tackle what has become “one of the great European problems”.
“We can’t think that this is a problem that only involves Italy, Greece, Spain, France and the southern European countries,” he said, imploring EU nations to work together.
Italy continues to save migrants despite ending its Mare Nostrum rescue mission, which was replaced by the EU’s considerably smaller Triton operation.
While Gentiloni said European countries are increasingly aware of the crisis, he called for EU efforts to reach beyond the boats.
“The journey from Eritrea to Italy is one of 4,000km. Often we concentrate on the final 50km, from the coast of Libya to Sicily or Lampedusa. Or what happens afterwards; from Sicily to Scandinavia.
“We should intervene in the horn of Africa, on human rights and the development of these countries,” the foreign minister said.
His comments reflect a broader shift towards focusing on migrants’ departure countries, including calls for registration posts to be set up for asylum seekers abroad.
Those who qualify would then be able to travel to Europe without having to make the dangerous boat journey, Christopher Hein, director of the Italian Council for Refugees (Cir), told The Local earlier this year.
At least 3,300 people have died attempting to reach Europe by boat so far this year.
The Italian Navy rescued 160,000 migrants in just 13 months of its Mare Nostrum operation, at a cost of around €9 million a month.